1. Field of the Invention
The invention relates to an onboard motor controller.
2. Description of Related Art
There is a conventional electric vehicle that is provided with an electricity storage device, such as a secondary battery or a capacitor, and that travels by driving an electric motor, which serves as a traction motor, using driving force generated from electricity stored in the electricity storage device. Examples of the electric vehicle include a hybrid vehicle and an electric automobile. The electric vehicle includes a motor controller that determines whether the rotational state of the electric motor is appropriate on the basis of a command value and drives the electric motor on the basis of the determination result.
As described in Japanese Patent Application Publication No. 2009-254119 (JP 2009-254119 A), the motor controller includes, as a device that detects a collision of a vehicle in order to execute a failsafe process at the time of the collision of the vehicle, a device that determines whether an abnormality due to the collision has occurred in the electric motor on the basis of for example, phase currents or phase voltages of the electric motor and that executes a process of stopping the driving of the electric motor when it is determined that an abnormality has occurred. Japanese Patent Application Publication No. 6-245323 (JP 6-245323 A) describes that when an acceleration sensor detects a high acceleration and thus a collision of a vehicle is detected, a supply of electricity to an engine computer and an electricity generator controller is blocked to stop the driving of the engine and a supply of field current to the electricity generator.
In an electric vehicle provided with the motor controller, electricity may be directly supplied to the motor controller through the use of a high-voltage traction battery that is a high-capacity electricity storage mechanism. When a collision occurs while the electric vehicle is travelling, it is necessary to immediately block a supply of electricity to the motor controller to stop the driving of the electric motor and to stop the driving of the engine and a supply of field current to the electricity generator in order to avoid a risk that electric shock will be given to a driver due to a high-voltage or occurrence of a fire due to heat generated from the electric motor. In order to stop the driving of the electric motor, on the basis of the information within a motor control system including a current sensor, the control mode of the motor is switched from voltage phase control by rectangular wave driving (one-pulse control) adopted to enlarge a driving range at a high rotational speed, to current vector control based on a sinusoidal pulse width modulation control (hereinafter, abbreviated to “sinusoidal PWM control”) in a low rotational speed region. However, with the above-described method of switching the control mode, the switching time becomes longer depending on a motor constant and it takes a long time to receive a response of the current sensor or to determine a detected current. This raises a possibility that, at the time of a collision, it will not be possible shift to a failsafe process within a short period of time.